This probably won't help you too much, but I also had this issue. Tried everything to clean it off with zero success this spring and the other day noticed the pink was gone. I'm not sure what did it, but my thought is that it must have been airing the boat out well in the garage after every use (the previous owner did not do this). It's a weird deal, but I'm happy to see it go.

First of all, beware goingto the dealer about the pink spots. The warranty on mastercraft specifically excludes the pink stains, which is something that is 'created' by an organism. I hope that mastercraft will consider modifying their vinyl formulation to have more biocide, as per the info below. But the solution I mention below worked on my non-MC boat, should work on your vinyl issue. I posted about this on mymastercraft.com at one point, http://mymastercraft.com/Forum/view_...m=3&category=2, here's the info:

"I did some research on the pink stain that emanates from the stitching a while back. Biocide in the foam or vinyl is supposed to help prevent this, but it doesn't always help enough.
- boat vinyl and the organism known as Streptoverticillium reticulum creates the pink dye, and loves to live with vinyl. And there's even standards to evaluating the performance of vinyl against these "pink staining microbes". For example, http://www.astm.org/cgi-bin/SoftCart....htm?E+mystore and sources such as http://www.springerlink.com/content/g31n5p5659686322/ provide info to help prevent these fungi during the Vinyl creation, etc.

Just put soft-scrub (with Bleach, not the regular version) on your finger, and liberally rub it on the stain. Its just a bathroom tub & tile cleaner with bleach in a gel/paste form making it easy to apply and not 'run'. Leave it in the sun all day. Next day, wipe it off and repeat. Do it a few days, and sure enough, the pink gradually disappears. It really works! As always, do a test spot to make sure the bleach doesn't effect your colors. When its all prepared, put 303 or other protectant on it, but frankly, it feels smooth and protected even though you've killed the microbes and removed the stains they left behind.

I do recommend though that you not put it on the same finger each day but on maybe a small rag, since it actually can burn your finger after a few days, make it numb, etc. "